Waveform modifying device



UTILIZATION DEVICE .Y m% A MC F m E B O R A TTORNEYS R. F. CASEY Filed June 23, 1954 LOAD LINE 0 GRID VOLTAGE( Ali n A April 15, 1958 WAVEFORM MODIFYING DEVICE Z, A Emma 95 c SIGNAL SOURCE .4

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Uflitfifd tates Patent WAVEFORM MODIFYING DEVICE Robert F. Casey, Pompton Plains, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. 1., a corporation of Delaware Application June 23, 1954, Serial No. 433,794 Claims. (Cl. 250-27) This invention relates to the production of rectangular pulses which are useful for many purposes such as in blanking, gating or switching circuits.

As is well understood in this art, if a long rectangular pulse is applied to the grid of an electron discharge tube through blocking condensers, the charge appears on the grid only momentarily because it leaks off through the grid-leak-resistor usually employed with such a device.

The capacitor and resistor form an RC circuit which difierentiates with characteristic distortion unless the time-constant thereof is ten times as long in duration as the pulse. Since the value of the grid-leak-resistor R is limited in value by the design of the tube, the capacitance C required for a realistic time-constant may exceed 200 microfarads and may be exposed to potentials as high as 30,000 volts. As is well known, these conditions necessitate a large bulky expensive capacitor.

Broadly speaking the present invention involves the use of a gated-beam tube such as is designated a 6BN6 tube-in a novel manner to overcome these difiiculties.

Inview of the foregoing the following could be stated to be some of the objects of this invention;

(a) To provide a circuit which produces a square or rectangular pulse;

(b) to produce a square wave with a minimum of external power;

(c) to produce the pulses at very high frequencies;

(d) to produce square waves over a great range of frequencies;

(2) to produce a square wave from a distorted pulse, a sweep voltage or any voltage varying over a fixed range;

(I) to eliminate the need for a large, bulky, expensive, high capacity capacitor;

(g) to produce a circuit having an infinite time-constant.

As the disclosure proceeds other and more detailed objects will become apparent to those skilled in the art.

The principles of this invention are explained herein in connection with the accompanying drawings, in which Figure 1 is a graph of grid current-voltage relations in a gated-beam tube;

Figure 2 is a graph of the various input waveforms shown in broken lines as related to a rectangular pulse output waveform produced therefrom in accordance with this invention; and

Figure 3 is a schematic showing of the circuit relationship by means of which the results of this invention are produced.

Referring first to Figure 3, there is indicated diagrammatically at 9 a source of signal pulses which may have a wide range of waveform such as those indicated in broken lines in Figure 2. The source 9 is coupled through a capacitor 24 to the input of a utilization device 26 of any type such as for example a cathode ray tube, the coupling through the condenser being made to the brightness terminal of the tube circuit.

At 10 is a gated-beam tube such as a 6BN6 multielectrode vacuum tube having a cathode 12, a limiter grid 13, an accelerator electrode 15, a quadrature grid 11, and an anode 17. The anode 17 is directly connected to the cathode 12 through a suitable potential source 14. The accelerator electrode 15 is connected between the anode 17 and the potential source 14 and the limiter grid 13 is connected between the cathode and potential source 14. The cathode 12 is connected through the usual resistor to a biasing potential source 18, a variable resistor 23 and a fixed resistor 22 to the quadrature grid 11. The quadrature grid 11 is also Connected to the input terminal of the utilization device 26 by means of the conductor 16.

Before describing the operation of this circuit consideration of the following matters will be helpful. A study of Figure 1 illustrates the fact that a gated-beam tube behaves like a complex resistor which has two stable states A and B, separated by a region of instability in which the tube exhibits negative resistance characteristics. The upper and lower critical points C and D occur where the slope of the dynamic characteristic is the same as the slope of the load line but opposite in sign. This curve is determined by the tube structure and its electro-optical properties which need no further discussion here.

During the operation of such a tube the grid voltage remains at A until an initiating voltage, which may be a sweep, a quasi-rectangular pulse, or some other:

wave form, drives it past the point C to the point B, Where it rests in a stable state. A similar result occurs when the voltage decreases to drive the grid past the point D to the ing through the voltage C and decreasing through the voltage 1) will produce a rectangular wave, as illustrated in Figure 2 by the solid line rectangular pulse. The quasi-rectangular pulse, indicated bythe dotted line shows the undesirable roll-ofi waveform usually obtained from the A-gate of a sweep circuit. The circuit herein disclosed corrects this undesirable waveform to produce a true rectangular pulse.

The input or initiating signal from the source 9 is applied to the grid 11 through the series capacitor 24.

The output is taken from the grid 11 and applied to the utilization device 26 which may be the brightness terminal of a cathode ray tube. The input grid 11 by reason of the inherent characteristics of the construction of tubes of this kind has an extremely small stray capacitance, usually about 6 micro-micro-farads. Since in this circuit the input is connected directly to the output without any intermediate tubes, amplifiers, multivibrators, or similar equipment, the only deleterious effect frequency-wise is the shunting by this extremely small stray capacitance. The frequency response at the output is therefore substantially equal to that at the input.

For the same reason the power requirements of this circuit are minimal when compared with those of the usual driven multivibrator which is capable of generating the same waveform comprising high frequencies and a short rise-time. Another advantage of this circuit is that it has practically no loading effect on its driver.

It may be shown mathematically that during the period of negative resistance the equivalent resistance R of this circuit is practically infinite, which accounts for the small power requirement. The time-constant RC is therefore also practically infinite, permitting the use of a small capacitor 24, and thus overcoming the drawbacks previously described with respect to the requirement of capacity, size and value. The mathematical conception point A. Thus, any waveform -ris-' of an infinite time-constant, is physically realized by the voltage resting indefinitely at the point B without any deviation from a rectangular output pulse. In effect this circuit could be called a two-terminal recurrent-waveshape-modifier, with the output very close to a square wave.

There is described herein a specific embodiment of the invention, but it will be apparent to those skilled in the art that modifications may obviously be made. I prefer, therefore, to be limited to the claims granted to me rather than by the disclosure hereof. i

What is claimed is:

l. A waveform converter combination for converting a nonrectangular pulse to a substantially rectangular pulse, consisting of a source of signal to be converted, a work circuit, a connection from said source to said work circuit including a capacitance, a gated-beam tube having an anode, a quadrature grid, an accelerator electrode, a limiter grid and a cathode, a direct connection between said anode and said accelerator electrode, a direct connection between said limiter-grid and said cathode, a source of positive potential connected between said anode and said cathode, a connection from said cathode to said quadrature grid including a resistor, a second potential source, and a variable resistor, a connection from the junction of said second potential source and said variable resistor to ground, said connection acting as a second terminal for the input signal, and a connection from said quadrature grid to the connection between said source and said work circuit.

2. A waveform modifying circuit for producing rectangular waveforms comprising: a gated beam tube having an anode, a quadrature grid, an accelerator electrode, and a cathode; a direct connection between said anode and said accelerator electrode; a first source of potential connected between said anode and said cathode; a second source of potential having a negative terminal and a positive terminal; a connection between said negative terminal and said cathode; a resistor connected between said positive terminal and said quadrature grid; a circuit terminal connected to said quadrature grid; means for applying between said terminal and said cathode signals whose waveform is to be modified; a utilization device connected to said terminal, whereby said terminal serves as an input terminal for said signals, and as an output terminal for said rectangular waveform.

3. The circuit of claim 2 wherein a blocking capacitor is connected to said circuit terminal.

4. A waveform modifying circuit for producing rectangular waveforms comprising: a gated beam tube of the 6BN6 type having an anode, an accelerator electrode, a quadrature grid, a cathode, and a limiter grid; a direct connection between said anode and said accelerator electrode; a first source of potential having a positive terminal connected to said anode, and a negative terminal connected to said cathode; a second source of potential having a negative terminal and a positive terminal; a resistor connected between said negative terminal and said cathode; a variable resistor connected between said positive terminal and said quadrature grid; means including a coupling capacitor connected to said quadrature grid, to transmit to said quadrature grid signals whose waveform is to be modified; means including a connection between said limiter grid and said first source of potential, to maintain said limiter grid at a potential near to andsubstautially constant with respect to said cathode; and a utilization circuit connected to .said quadrature grid; whereby said quadrature grid serves as an input electrode for said signals, and as an output electrode for said rectangular waveform.

5. A bistable flip-flop circuit element for producing rectangular pulses from an input waveform, comprising:

a gated beam tube of the 6BN6 type having an anode, a quadrature grid, and electron beam producing means;

means to bias said quadrature grid; a terminal connected to said quadrature grid; means causing said element to flip from one stable state to another, said means comprising means to apply said input signal to said'terminal; and means to obtain said rectangular pulse from said terminal whereby said terminal acts as both an input and an output terminal.

References Cited in the file of this patent UNITED STATES PATENTS 2,060,095 Mathes Nov. 10, 1936 2,115,881 Roosenstein May 3, 1938 2,450,443 Rich Oct. 5, 1948 FOREIGN PATENTS 573,508 Great Britain Nov. 23, 1945 OTHER REFERENCES Electronics, February 1950, pages 82 to 85, "A Gated Beam Tube, by Robert Adler. 

